The far right in the US take a very isolationist stance on foreign matters and simply don't care. I don't understand your reasons for disliking the US. Both in South Vietnam and South Korea they came to the aid of an ally that asked for their help. Many people also fail to remember that the US army had a presence in Vietnam before the war even started, The French allowed them to built airforce bases there in WW2.
The far left and far right both are isolationist in their views. The far left and right disagree on social issues and economics.
Even if one hates the US, it is irrational to applaud people being harmed because you perceive it as harming US interests. The fake narrative was created by anti-American revisionists and socialists that the RVN wanted the communist takeover and that the US stood in the way of this nationalistic movement and that is the narrative NGB is pushing.
The US didn't want Indochina restored to French control but the UK and France got the US to relent. The US first choice was for China to take responsibility.
Popular history has it that Ho Chi Minh did a lot against the Japanese and aided the US a great deal but the reality is he did little and had only a few insignificant dealings with the US.
His rag tag communist forced declared independence though they took over control of just a few areas where the Japanese pulled out of because of their surrender. The Japanese gave them their weapons and some even stayed on and trained them. The Chinese took over these Northern areas on behalf of the allies and Ho's men fled. The Japanese remained in control of the South. Eventually the French forces were freed and the Chinese and Japanese left and the French took over Indochina.
Vietnam was divided into 3 parts under French rule. This is because the people in the areas were so different. There were plenty of minorities as well. The notion of their being a single Vietnam was a complete fiction made up by revisionists it was a hodgepodge more like Yugoslavia. That is one of the reasons why China didn't want permanent responsibility for the area.
There were many different groups that wanted independence. The communist killed the leaders of the groups and basically took control of all of them in such manner to turn it into a communist movement.
After the communist takeover of China the communists armed Ho (with a lot of the weapons they captured from the Nationalist forces that fled to Taiwan they left their weapons behind and is why they had many Western weapons) and that is when his followers began in earnest to fight the French.
The US provided military aid to the French. The French public got sick of it and decided to leave. That is when the US was asked by South Vietnam for direct aid. Popular fiction is that the US installed a puppet but that is not true we supplied the government that formed under the peace deal that resulted in the French leaving. Nor is it true that the Vietcong was a South Vietnamese entity. The organizers were all from North Vietnam they infiltrated into South Vietnam. Until 1960 it was mainly a terrorist campaign. Then it escalated into regiments and even division from North Vietnam operating there. Some were NVA AKA North Vietnamese regulars. Others were Vietcong regiments which the cadre (officers and noncoms) North Vietnamese soldiers and the rest were a mix of people who came from North Vietnam or were in South Vietnam already but were impressed into service willingly or unwillingly.
The Vietcong were absolutely decimated after the Tet Offensive. Teh Tet offensive was a major conventional attack. The counterattack from the US and RVN forces wiped out most of these forces. The remainder of the cadre were largely killed during US counterinsurgency operations. The few Vietcong regiments that remained failed miserably in operations in 1970 and 1971 and basically after that they were discontinued. They were reconstituted in name only by naming some units of the North Vietnamese Army Vietcong regiments.
Post Tet the ARVN units began to fight much better than in the past. They essentially copied the US military- they even had Vietnamese Marines, Rangers etc. They had some Americans helping lead them but began carrying on most of the fighting themselves with US airpower assisting them. The North Vietnamese suffered comparable casualties against them that the US inflicted. The ARVN was suffering considerably less casualties than the enemy. This meant there was a stalemate. This and US bombing of the North forced the to give up and agree to a peace deal.
In order to get South Vietnam to agree to peace Nixon secretly promised that if the treaty were violated we would assist them again. We stuck to the treaty and cut our aid to the RVN. The USSR and China began providing much more aid than in the past particularly the Chinese they flooded Vietnam with weapons even tanks and planes. They helped build a million man army. They didn't do it for nothing. They did it to enable the communist government to take over all of Vietnam.
They knew from the past that US airpower would decimate their large scale attacks so they started out with a limited attack that the South Vietnamese was dealing with but they were low on fuel, ammunition and asked the US not only for such aid but for US airpower assistance. Nixon was busy with Watergate and had no intention of going back because it would mean the need to stay committed forever like in Korea. Vietnam had no strategic value that he deemed would warrant such commitment. So he rebuked the. The Vietnamese saw the US refused to reengage and then launched a full scale invasion. Without US advice their planners responded ineptly. But even when they did know what to do try a counterattack fuel problems or refugees blocking the roads stood in their way. Many soldiers went home to try to defend their home villages instead of staying with their units. Obviously they would be totally ineffective in small bands against a massive conventional force. They managed to hold out longer than the French did against the Nazis but that's not much of a feat!
The US military was defeated fiction is just that a fiction. The lesson enemies got from this is that eventually the US will tire and leave and then after the US is gone they can renew the struggle. This is the strategy Saddam had in mind that is why he organized an insurgent force even before the invasion happened. He didn't expect to be caught and killed. It's the strategy the terrorists in Iraq had in mind. It's the strategy the Taliban still have in mind. Of course the North Vietnamese had something the Taliban currently lacks. The Taliban were initially supplied by Pakistan but their aid now is not from government entities but simply ordinary Pakistani extremists. That's far different from the DRV being supplied by China and the USSR with heavy weapons. They can still do damage to various villages and towns but have little hope of taking over all of Afghanistan.
